Used oil represents a major environmental problem. For example, in 1992, the U.S. Environmental Protection Agency estimated that of the 4.9 million cubic meters (1.3 billion gallons) of used oil produced annually in the United States, only about 2% was being re-refined, despite the existence of a large number of physical and chemical processes developed for reclaiming or re-refining industrial and automotive lubricants. The remainder of the waste oil, presumably, was being dumped or discarded into the environment in various ways.
An early major treatment process involved re-refining waste oil with sulfuric acid and clay. Sulfuric acid acts as an extraction medium for the removal of unsaturates, dirt, additives and colored materials from the waste oil. The clay is used as an adsorbent to remove impurities. Disadvantageously, in this process, large quantities of spent acid sludge and clay are produced and must be disposed of as a process waste.
In order to avoid the waste disposal problems from acid-clay processes, different types of distillation processes have been developed, for example, as disclosed in U.S. Pat. No. 3,625,881 and U.S. Pat. No. 4,071,438. These processes produce a recycled lubricant as a major product and a carbon-black slurry as a process waste.
Recently, the development of a process for reclaiming useful fuel has resulted in the production of diesel fuel from waste oil, as disclosed, for example, in U.S. Pat. Nos. 5,271,808 and 5,286,349. U.S. Pat. No. 5,271,808 discloses a process for reclaiming waste oil wherein a vessel heater is used. In this process, because a large volume of feedstock is held in a heater vessel under high temperature for a long residence time, undesired polymerization, oxidation and dehydrogenation take place, resulting in the production of an unstable diesel fuel and a large volume of ash cake residue. Additionally, the run length of the process is quite short.
DE-A-3,224,114 discloses a process and apparatus for cracking used motor vehicle engine oil by heating with microwaves. The used oil cracks on heating to the distillation point. The volatile products are removed in a condenser.
JP-56 082886 discloses a process to suppress local coking and to improve the yield of light oil, by mixing a catalyst with a heavy oil to form a uniform slurry. The slurry is cracked in the liquid phase catalytically.
EP-0 308669 discloses processing materials containing halogenated hydrocarbons by pyrolysis in a fluidised bed of basic substance.
U.S. Pat. No. 5,143,597 describes a used lubricant oil recycling process in which a used lubricating oil is injected to a delayed coker downstream of the coker furnace whereby the used oil is thermally cracked into hydrocarbon fuel products.